1. Field of the Invention
The present invention relates to a process and apparatus for forming rubber bodies and, more specifically, for forming rubber bodies such as tubes during vulcanization.
2. Background Information
French Patent No. 2,548,086 describes a process for the fabrication of a profiled rubber tube using extremity molds called "cylindrical molding caps" which are made of stainless steel or a mild steel.
In the same document, there is a description of a removable cylindrical holding cap which is made of a rubber material, but this element is in no way intended for the molding of the extremities of the tube. This patent specifies that the removable cylindrical molding cap is to be placed on the other portion of the extremity of the mandrel so as to exert an axial compression force on the unvulcanized rubber tube.
The molding of the extremities of the flexible tube is, thus, realized by a rigid cylindrical molding cap, and not by a radially deformable skirt made of a vulcanized elastomer compound as in the instant application. Therefore, French Patent No. 2,548,086 can not be considered pertinent to the instant application.
French Patent No. 2,195,935 relates to a device for molding objects by means of an inflatable, flexible mold and, thus, requiring the utilization of fluid for the inflation thereof.
French Patent No. 2,518,014 (Class A) describes, in a very general manner, a process for the realization of a "bent flexible conduit" in which the extremities of the blank are fixedly held in relation to the mandrel or are clamped onto it by rigid means. The process described in this document is, therefore, only part of the technological background of the invention which is the subject of the instant application.
The present invention relates to the fabrication of flexible tubes which may be used for connecting two terminals of a cooling circuit on a motor or on other machines, such as the connecting elements intended for use on automobiles, but generally, for use in any circulation of fluid in industrial, agricultural or similar equipment.
The invention relates, in particular, to the making of sections of curved tubes, which are specially shaped to fit crowded passages. These sections of tubes are produced by vulcanization of an elastomer such as a polymer, an elastic rubber or a like substance in the form of a tube or tubing piece. The tubing piece to be vulcanized is preferably formed by an extrusion process and, then, subsequently threaded over a mandrel for further processing.
Supplying parts to the automobile industry, due to the demand for the mass production of the components used, requires the selection of the most economical process for the fabrication of products to perform a function, even if the products can also be made in other somewhat more expensive ways. Thus, the molding of rubber tubes having complex shapes, although possible to manufacture, has virtually been completely replaced, for reasons of economy, by the pre-formed tubes. These pre-formed tubes or hoses generally comprise an internal tube, quite often reinforced by braided or knitted fabrics, or by the continuous wrapping of textile fibers. The passage of the reinforced internal tube through an extruder with a square-die makes it possible to cover this reinforcement with an elastomer coating. This operation, usually performed continuously, is followed by the cutting-tolength of the at least partially unvulcanized tubing, which is then forcibly engaged over a mandrel; thus, giving the tubing a definitive desired shape. The tube is then vulcanized and disengaged from the mandrel by the use of a force.
This process for the fabrication of tubular connecting elements, which is very widely-used, is followed, as necessary, by a reinforcement of textile adhesive tape, with or without cutting-to-length, as a function of the required precision and surface quality of the outer surface and/or end of the tube, and as a function of the utilization requirements. Since, in the majority of cases, a collar is used to secure the attachment to the terminal, the manufacturers generally desire a degree of precision in the thickness, the surface and the positioning of the extremities. This precision can not always be achieved by the vulcanization process, without the use of a mold, in the autoclave, or other furnace used for vulcanization.
Various improvements aim at locally refining the geometry of these extremities, without changing over to the excessively expensive mass production molding of such voluminous parts, since the parts are usually reinforced with textiles to increase their rigidity or their bursting strength. One of the most recent processes is disclosed in Soviet patent SU 1,331,660 (KHOMSKOV), in which the mechanization of a ramp carrying several curved mandrels, after the flexing of the tubular blanks, makes possible the simultaneous vulcanization in an autoclave of several identical connection elements.
The internal surface and the surfaces of the extremities are supported during the vulcanization and, therefore, have a surface quality which is better than that obtained by means of the so-called "free state curing" process, and thus eliminates the need for a subsequent cutting-to-length process. This process of the prior art, usually, does not improve the regularity of the outside diameter or the thickness of the connection element or the quality of the external surface of the tubing piece.
The East German Patent DD 249222 (VEB GUMMIW.THURINGEN) discloses a process for molding raw tubular blanks in female molds using an internal gas or liquid pressure. This process can ensure a good exterior surface quality, but it does not solve the problem of the ovalization of the connecting elements or the problem of maintaining a constant thickness. The process, also, requires the utilization of molds which are heavy, on account of their large dimensions, and does not have the advantage of the high vulcanizing pressure customary in molding, since the pressure used in the technology described is only steam pressure.
On the other hand, Japanese Patent J62-256.414 (TOYODA) discloses an internal mandrel terminal which makes it possible, during vulcanization, to shape the spread extremities of a tube by vulcanization in an autoclave. Here again, the process does not solve the problem of achieving a constant thickness.
Japanese patent J62-019.414 (TOKAI RUBBER) relates to threading a blank or tubing piece on a molding mandrel. It discloses the fastening at each extremity of a cylindrical sleeve, inside of which are two jaws which are closed on the blank or tubing piece by means of screws. These jaws are engaged over the mandrel and make it possible to shape the rubber piece, as desired, by the partial molding of the exterior surface, such as the molding of flanges designed to hold a collar.
The assembly operation of the above mentioned art, using screws, and the removal operation after vulcanization in the autoclave are accompanied by the well-known problems of molding, without utilizing the advantage of a high pressure. The process can provide a satisfactory, exterior shape, and can verify correct centering in relation to the internal mandrel. However, this process does not assure that the material will fill the entire mold. For example, a burr between the two halves of the mold can interfere with the installation of a collar, or can necessitate a deburring operation.